Our Course Catalog at /SitePages/CourseCatalog.aspx disappeared.

We've checked the version history of that specific page in case someone had deleted anything but in all versions it seems not working. What could be the matter?

Answer:

Someone must have deleted the Course catalog web part on the page. To add it back you would need to get a .dwp file of the web part from another REM site, upload it to your REM site and add the web part back to the page.